1. Field of the Invention
The present invention relates to an adhesive resin composition having high speed moldability, thin moldability, low neck-in property, high draw-down property, excellent heat sensitive adhesion, and excellent calendering and exhibiting strong adhesion properties with a substrate composed of a polyester, polyamide, metal foil (e.g., aluminum foil), etc., in particular, a polyester, and also relates to a laminate having a layer composed of the adhesive resin composition and a process for producing the same. This laminate can be used as packaging such as food packaging.
2. Description of the Related Art
Polyolefins such as polyethylene are excellent in heat sealability and moisture-proofing and is easy to extrude, and therefore, has been used as a single layer film, sheet, or material for shaped containers and also has been widely used in, for example, a packaging field as a laminate with various resin films and sheets, metal foils such as aluminum foil, paper, etc. However, polyolefins are inherently nonpolar and has the defect of poor adhesion to different materials, in particular to polar materials such as polyamide, polyester, aluminum foil. Accordingly, various methods have been proposed to form a multilayer laminate using polyolefins.
In order to produce a laminate of polyethylene and polyamide, for example, the following methods using a modified polyolefin rather than the polyethylene alone have been utilized:
(1) The so-called co-extrusion method of melting a modified polyolefin obtained by graft polymerizing an unsaturated carboxylic acid or its derivative onto polyolefin, an ethylene copolymer obtained by copolymerizing ethylene and an unsaturated carboxylic acid or its derivative, or a composition comprising these polymers and a polyolefin with a polyamide resin and extruding the same from a die to obtain a laminate, PA1 (2) The method of preparing a polyamide film in advance and extrusion laminating (or coating) it with a blend of polyethylene and the above polymer, PA1 (3) The method of co-extrusion laminating a polyolefin and the above polymer on a polyamide film. PA1 (A) at least one component selected from the group consisting of (i) polyolefins having a melt flow rate of 0.1 to 30 g/10 min and (ii) olefin polymers having at least one functional group capable of reacting with an epoxy group; and PA1 (B) an epoxy compound having at least two epoxy groups in the molecule and having a number average molecular weight of 3000 or less, the ratio of the weight of component (B) to the total weight of the components (A) and (B) being 0.01 to 5%.
Further, in order to produce a laminate of polyethylene and polyester, there has been proposed the method of using a polymer obtained by grafting glycidyl methacrylate or allylglycidyl ether etc. onto a polyolefin or by copolymerization with ethylene and co-extruding with a polyester or co-extrusion laminating a substrate such as a polyester film.
These methods, however, may give a bond strength in the case of co-extrusion, but cannot give a sufficient bond strength in the case of lamination for laminating on a substrate such as a film, sheet, or paper.
In particular, it is difficult to obtain a laminate having a strong bond strength with, for example, a polyester based substrate.
In order to improve the bond strength, there is the method of raising the temperature at the time of formation, but the polymer is poor in heat stability and decomposes therefore, there is the problem of an odor and fumes at the time of formation. Further, there is the problem of an odor remaining in the laminate product.
As another method for improving the bond strength, there is the method of applying a corona discharge to the substrate. However, in this case, it is necessary to separately prepare a special equipment(s). Also, the bond strength with the substrate is not sufficient.
Furthermore, in order to improve the adhesion, the ozone treatment method of blowing ozone on the resin discharged from the die to cause the surface to oxidize has been used. The ozone treatment has the advantage of enabling oxidation of just the surface requiring the adhesion at a low temperature (Japanese Unexamined Patent Publication (Kokai) No. 57-157724). However, ozone has the problems of odor, corrosiveness, etc. and is still limited in use. Furthermore, the level of the bond strength is still insufficient. In particular, since the laminate absorbs moisture, there is the problem of a large decline in the bond strength.
As a reliable method for obtaining the sufficient adhesion properties with the substrate an adhesive known as an anchor coating agent (or primer) is jointly used.
This method uses an adhesive layer interposed between the substrate and the laminate resin. As the adhesive, an adhesive such as of the imine type such as polyethylene imine or the urethane type is used. In general, a urethane type adhesive is widely used as due to the high bond strength thereof. However, in this method, while a high bond strength is obtained, the coating process is complicated. Further, an organic solvent is used. Therefore, there are also problems in safety or the working environment. Further, it is necessary to prepare the solution of anchor coating agent and wipe off the anchor coating agent adhering to the rolls, so there is the problem of a major reduction in the operation efficiency.
Furthermore, methods of introducing an acid anhydride group, carboxyl group, etc. into the polyolefin are also proposed (see Japanese Unexamined Patent Publication (Kokai) No. 57-133055, Japanese Unexamined Patent Publication (Kokai) No. 59-75915, etc.). However, according to these methods, the adhesion properties with a polyester are insufficient and it is impossible to directly bond to a polyester by extrusion lamination.